In the applicant's U.S. Pat. No. 5,167,421 which is entitled "Safety Seat Equipped in Automobile" and filed on Jan. 5, 1991, a safety seat is disclosed. The seat is supported with four ball rollers in pipe rails. In a normal state of the seat, the springs in front of the seat are compressed, a common electromagnetic locking arrangement locks the seat, and several separated sensors are arranged on the parts of the motor vehicle being prone to be collided with. When a collision takes place, the sensors are damaged to deform to have power on and the electromagnetic locking arrangement removes the pin inserted and have the seat released.
However, the safety seat with above structure has the disadvantages that the freedom of the ball rollers in the pipe rails is not satisfied. Further, under the state of the springs being compressed, it is difficult and requires great electromagnetic force for the inserted pin to be pulled out. That is, much electric current is required to generate an electromagnetic force.
Accordingly, the object of the invention is to provide an improvement of the cited seat. The seat unit provided by the present invention adapts four ball bearings to bring about the satisfied freedom of movement of the seat, and an improved locking arrangement which, with satisfied locking effect, requires less electric current to pull out the locking member and to release the seat.